In recent years, servers and other electronic apparatuses have been made higher in speed and more advanced in functions. Such electronic apparatuses mount large numbers of electronic devices. These electronic devices generate heat along with their operation. One of these electronic devices, the CPU (central processing unit), is now consuming increased power due to its higher speed and more advanced functions. The amount of heat generated by a CPU tends to increase the greater the supplied power. Further, in general, a server mounts a plurality of CPUs. The amount of heat which is generated from these becomes tremendous. If the heat causes the inside of the server to become high in temperature, the functions of the electronic devices will become impaired and malfunction of the server will be caused. Therefore, to maintain the functions of the electronic devices and avoid malfunction of the server, the heat generating electronic devices need to be cooled.
As a radiator which takes heat from heat generating electronic devices and discharges it to the outside, there is known a liquid cooling system which runs coolant through coolant piping and uses its passage so as to take heat from the electronic devices and discharges the heat to the outside (for example, Japanese Laid-Open Patent Publication No. 5-109798 and Japanese Laid-Open Patent Publication No. 2005-381126). A liquid cooling system in general is provided with heat receiving units, a radiator, pumps, a manifold, and a plurality of pipes which connect these with each other to form a closed path. The heat receiving unit takes heat from the CPUs using the coolant, while the radiator discharges the heat of the coolant which has become high in temperature due to the taken heat to the air or other outside part. The coolant which flows through the channels which are formed by the piping is supplied with the force for running through the channels by the pumps. The manifold divides and merges the coolant which flows through the channels.
In this regard, since a liquid cooling system has such a plurality of components, when applying the liquid cooling system to a server, since there is a limit to the space inside of the server, the layout of the components inside the server has to be considered or else mounting is not possible. Further, in a server, an air cooling system which uses fans is mounted for cooling the electronic components other than the CPUs. The fans are used to take in outside air as the cooling air so as to cool the electronic components and to discharge to the outside the cooling air which has become high in temperature due to the taken heat. For this reason, if mounting a liquid cooling system in addition to the existing air cooling system, there is the problem that the flow of the cooling air which is supplied by the air cooling system will be blocked by the components of the liquid cooling system and cooling will be obstructed. Mounting has therefore been difficult.
Furthermore, a server or other electronic apparatus is installed in a data center or computer room or other cramped location, so the places where it can be installed are limited. To enable a large number of servers to be installed in such limited locations, reduction of the server size and reduction of the area occupied at the time of installation are sought. In this regard, in recent years, servers have been expanded in functions and performance, so the work, calculations, etc. which used to be performed by a large number of servers can now be performed by a smaller number of servers. Also, individual servers have also been improved in performance, so the area which the hardware occupies has been reduced. This improvement of the functions which the servers can perform and improvement of the performance of the servers have led to higher density mounting of electronic components in the servers. When mounting electronic components in servers at such a higher density, the issue arises of how to efficiently cool the heat generating electronic components.